Particularly in the nuclear field, hazardous environments are being isolated by weld-sealing them into containers. This may be an overly broad statement. More subjectively, there are many parts in and about a nuclear reactor installation which must be isolated to preclude the escape of radio-active material into the environment. Some portions, or all, of a nuclear reactor are placed in containers which are seal-welded to prevent the escape of reactive material. Obviously, the seals must be highly efficient. What may not be quite so obvious, is that the mechanism necessarily placed within the container has to be periodically inspected, maintained, and replaced. Briefly, the highly important seal of the container must be removed in such a way that it can be subsequently replaced.
In the large majority of industrial installations, when two surfaces are seal-welded, there is no need to consider subsequent breaking of the seal and reforming the seal. There are many small sealed mechanisms with which the end user is not expected to tamper. If the mechanism sealed in its container malfunctions, it is usually expected that it will be replaced--seal, housing, and all. The advent of the huge nuclear reactor installation exemplifies the change which is now taking place.
There are parts of the nuclear reactor and its control mechanism which, for safety reasons, must be isolated in containers. These are not relatively simple plug-in modules. Therefore, the containers are designed with two surfaces whose edges are welded together with the required sealing efficiency, but which must be unsealed to get at the mechanism within.
Removal of a sealing-weld bead is, broadly, a matter of applying a cutting tool to the bead to cut away the material of the bead. In contrast to the normal destructive technique, the material of replaceable beads must be removed carefully, preserving the integrity of the seal-welded surfaces so that their edges may be resealed to each other with a resealing weld bead.
Cutters to remove the material of weld beads do not have highly esoteric configurations, nor are these cutters actuated in any peculiar way by motive sources. With respect to the nuclear radiation environment, they may be operated remotely, but their actual application to the seal-weld is straight-forward. The important aspect of the actuation of the cutter bit is that it must be limited in the depth to which it is lowered. It must penetrate the weld bead to a predetermined depth to avoid deformation of the edges of the container surfaces sealed by the weld bead, while yet shaping the edges for rewelding.